Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Summer 2014
4 The Fluid Journal Summer 2014 In California, there are no miracle cures. Leaching is only remedy when using saline irrigation water. Summer 2014 • Vol. 22, No. 3, Issue #85 There are two four-letter words Californians just can’t seem to get enough of: rain and snow. For a third consecutive year, sub-adequate rainfall and, more importantly, scant Sierra snowpack have left the state’s storage reservoirs at just 53 percent of capacity statewide. And with the Sierra snowpack at just 16 percent of normal, the opportunity to further raise lake levels significantly through spring and summer melt is dim to nonexistent. Drought status California’s water supply is very short and must be balanced to meet the competing needs of cities, the environment, and agriculture. Federal and state surface water deliveries to the thirsty San Joaquin Valley, slashed originally at 0 percent, have been upgraded to a less than impressive 5 percent of normal. The impacts will be far reaching with an estimated 500,000 to 800,000 acres of irrigated farmland looking for alternative water sources. Many acres of row crops, such as cotton, melons, vegetables, field corn, etc. , will simply remain idle. Cotton acres, for example, are expected to be at their lowest levels since pre- Depression days--just 190,000 acres. This is down about 100,000 acres from 2013. Growers of increasingly popular perennial crops, such as almonds and pistachios, are bracing for lower yields and reduced profits. Others are hoping they have or can find enough water to keep their orchards alive and their investments solvent. By Carl Bruice Summary: The last word of advice is to avoid miracle cures. There are none. Aside from reverse osmosis, there are no magic elixirs, magnets, ionizers or other devises that remove salt from irrigation water. The only remedy for continued use of saline irrigation water is leaching. Having your soil properly conditioned to take advantage of winter rains by treating the soil with calcium and high bicarbonate irrigation water with an acid will set the stage for effective leaching when winter rains arrive. The economic ripple will impact all industries and services that support and supply producers and those that transport, process, and market Ag commodities. Consumers can expect to pay more for food in the near future. Unemployment in farming communities greatly outpaces the state average. Tax revenues will fall from decreased farm gate proceeds and the industry that supports farming will be in decline. Few will likely be spared. As surface water availability decreases, growers are becoming more reliant on California’s massive groundwater reserves to meet production needs. But over-drafting of groundwater is a serious concern. The consequences are being felt now and will only become more acute in future years if current trends continue. One consequence of over-drafting ground water that is very troubling is a sinking of the Valley floor. An estimated 50 million acre-feet of ground water has been pumped and not recharged since 1962. As aquifers dry, ground sinks, and with their sinking, the very conveyance systems designed and built to deliver irrigation water during the arid summer months are at risk of failure. Salinity There is another danger that lurks with reliance on ground waters. Salinity. Much of the ground water in the Central Valley contains very high levels of dissolved salts, particularly in the west side of the San Joaquin Valley. Also, as groundwater levels in California’s coastal valleys drop, salt water intrusion threatens to seriously degrade the quality of these water resources. As more salty water is applied to farmland and less water is available for leaching harmful salts out of the root zone, the risk of crop injury and economic loss to the producer grows. Continued use of saline irrigation water without proper leaching jeopardizes the sustainability of hundreds of thousands of acres of California farmland (Figure 1). To illustrate just how rapidly soil salts can accumulate in the absence of leaching, consider that water having an ECw of just 1.0 dS/m (low), applied at 3 acre-feet annually, would add more than 50,000 lbs of salt per acre over a ten-year period! Thus, without adequate leaching, even waters of moderate quality can rapidly build the soil’s salts to disastrous levels. By definition, a saline soil is one that has an Electrical Conductivity of the soil extract (ECe) greater than 4.0 dS/m. Soil salinity levels above or below 4.0 may or may not be injurious to crops, so it is more important to know the salt tolerance of crops to be grown rather than what defines a saline soil. Table 1 presents salt tolerance data for some crops grown in California. Data are presented as the ECe (soil) and the ECw (water) that would be expected to cause yield losses of 10, 25, and 50 percent or complete crop loss as well as the maximum salinity levels for unhindered crop yield. This assumes a